Several problem areas need to be addressed when making color negative paper prints from color negative film images. The object of the process is to make a pleasing print from the film image. The first problem is to find the level of exposure necessary in a projection printer system to produce that pleasing print. In the simplest implementation of a process, one projects the color negative film image onto a photosensitive paper image receiver, processes the paper, and then repeats the process until a pleasing print has been obtained. In automated photo-finishing operations, a film scanner reads densities from the negative and passes the information to a computer algorithm that computes the appropriate exposure values so that a pleasing print can be obtained. At this point, the conventional photographic printing process ends. That is, if there are any remaining problems in a photographic image, no other simple processes are available to reduce the severity of the problem. Problems such as film under-exposure or over-exposure, inappropriate gamma for a particular scene, poor scene balance, and poor sharpness in the final image remain that we would like to correct or modify.
Optical printing of film under-exposures results in low quality images, the more under-exposed, the lower the quality. With the degree of under-exposure, the prints are low in contrast and maximum density. Under-exposures are common in available-light photography. Large over-exposures can also result in low contrast prints that are low in quality because film sensitometry tends to compress the scene highlights with significant over-exposure.
Methods and systems have been described for more than 10 years that are devoted to producing pictorial images on various media and devices from scenes captured on photographic film, via scanning to produce a digital image, image processing, and output rendering. Examples include the following.
Journal of Imaging Technology, Vol. 14, Number 3, June 1988, Firth et. al. describe systems that capture scenes on film, scan film to produce a digital image, digitally process the image, and output via a laser AgX printer.
U.S. Pat. No. 4,500,919, Schreiber discloses an image reproduction system that scans an image captured on film, displays the image on a video monitor, enables image processing, and finally output to an inked hardcopy.
U.S. Pat. No. 4,979,032 (Dec. 18, 1990, filing date: Dec. 27, 1988), Alessi et al. describe an apparatus, including a film scanner, an video monitor, image processing, and output, to produce various output visually matched to the image displayed on the monitor.
U.S. Pat. No. 5,267,030, issued Nov. 30, 1993, inventors Giorgianni et. al. describe method and means to transform images captured on film, via digitization on a film scanner, to a color metric or other space, with output onto a variety of media and devices. This document describes the improvements offered by digital image processing, including aesthetically pleasing modifications to the tone and color reproduction as well as sharpening.
U.S. Pat. No. 5,300,381, issued Apr. 5, 1994, inventors Buhr et. al. describe a pictorial imaging system that consists of capture on photographic film, film scanning to produce a digital image, image processing, and digital output.
U.S. Pat. No. 5,579,132, issued Nov. 26, 1996, inventor Takahashi describes an image processing system devoted to storing or producing images that have "substantially the same color" or additional "aesthetic color correction" versus the original scene, based on a variety of image processing transformations of the digitized image.
U.S. Pat. No. 5,608,542, issued Mar. 4, 1997, inventors Krahe et. al. describe a system that produces index prints based on scanning a film frame, image processing, and rendering.
U.S. Pat. No. 4,945,406, issued Jul. 31, 1990, inventor Cok, describes a system for achieving automatic color balancing of color images by transferring color pixel values from log exposure RGB color values into printing density values and generating color correction offset values utilizing a printing density based color correction method.
The KODAK 35 mm/24 mm color negative film format Index Printer, sold by Kodak, produces an index print (a matrix of small imagettes) reproduced from individual film image frames. The index print is produced by the photofinisher when the original print order is processed and is supplied to the customer as a convenient means of identifying image frames on the film (see: U.S. Pat. No. 5,608,542, above). The Kodak Index Printer uses image processing on the miniature images including:
digital image in film RGB printing density
applying a scene balance algorithm to balance the digital film printing density image
mapping the color negative digital image onto a color paper (EDGE-type) characteristic curve
digital sharpening
rendering using a CRT printer onto photographic paper
In the Index Printer, the above image processing: (1) is not applied to full frame images in a digital color printer; and (2) is not applied to high resolution images in a digital color printer, only low resolution images.
U.S. Pat. No. 5,134,573, issued Jul. 28, 1992, inventor Goodwin, discloses a method for increasing the range of values representing a color image which exhibit a linear response. The toe and/or shoulder regions of the film's three density vs. log exposure tables are straightened using look-up tables.
All of these articles or patents describe, in one form or another, processes for obtaining more pleasing prints from a film image capture than the conventional optical process. There is thus a need for a solution to these problems, which can be incorporated into a digital photofinishing system.